Applicant claims, under 35 U.S.C. xc2xa7119, the benefit of priority of the filing date of Apr. 16, 2002 of a German patent application, copy attached, Serial No. 102 16 986.1, filed on the aforementioned date, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method for testing a frequency converter, wherein individual switching elements of the frequency converter are selectively activated.
2. Description of the Related Art
In cases where a malfunction has occurred, methods of this type are used for the localization of a source of the malfunction.
Electrical drive mechanisms are employed in modem machine tools for the purpose of moving various machine elements in a controlled manner. Thus, drive mechanisms for shafts provide for the movement of the individual shafts of the machine tools into the required positions, spindle drives provide for the rotary movement of a tool, such as a milling head or a drill. For this purpose, a numerical control device converts the movements, which have been preset in programs, such as CNC programs, into positional set points, which are supplied to a regulating unit including position, rpm and current regulators. Voltage set points are generated in the current regulator, which are converted by a frequency converter by the so-called pulse width modulation. For this purpose, the phases of the motor are connected in the frequency converter with the positive and negative supply voltage via two switching elements. The switches are turned on as a function of the pattern of the pulse width modulation in order to generate the required voltage potential at each phase of a motor which is required for achieving the current set points.
There are numerous sources for malfunctions, which can lead to incorrect functioning, in a system which is constructed in such a complex manner. Methods are therefore known for detecting such malfunctions.
Thus, EP 0 848 492 A1 describes a method for detecting incorrect functioning of a drive system of the type described above. Individual phases of a motor are selectively charged with a set point current for this purpose. If the predetermined set point current has not been reached, it is assumed that there is a malfunction in the system. In this method it is disadvantageous that following the detection of a malfunction it is not clear where the malfunction is located. It is not possible to differentiate between a malfunction in the voltage converter and, for example, a short circuit or a line disruption outside of the voltage converter. Accordingly, there is a requirement for special methods, by which the ability of individual components, in particular the voltage converter, can be tested.
It is therefore an object of the present invention to disclose a method, by which the operativeness of a voltage converter can be tested.
This object is attained by a method for testing a frequency converter having individual switching elements and motor connectors for each phase of the frequency converter. The method includes selectively activating the individual switching elements of the frequency converter and applying a control pattern to a control input of each phase of the frequency converter. Registering voltage patterns occurring at the motor connectors for each phase of the frequency converter, wherein the registering is performed for each of the motor connectors via a single test line that is capacitively connected to the motor connectors. Comparing the control pattern applied to the control input with the voltage patterns registered for each phase of the frequency converter. Detecting a malfunction in the frequency converter in case of a deviation of the voltage patterns, registered at the motor connectors, from voltage patterns expected as a result of the control pattern applied to the control input.
A method for testing a voltage converter is now proposed, by which the operativeness of a voltage converter can be tested.
In a first step, individual switching elements of the voltage converter are selectively activated by applying a control pattern to the control input of each phase of the voltage converter. In the next step, the voltage pattern occurring at the motor connectors of the voltage converter is registered for each phase. Moreover, the applied control pattern is compared with the registered voltage pattern for each phase. In case of a deviation of a voltage pattern, detected at the motor connector, from the voltage pattern expected on the basis of the control pattern applied at the control input, a malfunction in the voltage converter is recognized.
Since very high voltages are present at the motor connector of each phase, these connectors must be galvanically separated from the device with which testing is performed. This is advantageously achieved in a very simple way in that the test lines are capacitively connected with the motor connectors. For this it might be sufficient to merely place the test lines near the motor connectors. It is furthermore possible by the described method to register all phases of the voltage converter by means of only one test line, which is capacitively connected to all motor connectors.
Further advantages, as well as details, of the present invention ensue from the following description of a preferred method by the drawings.